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Monday, November 12, 2007

Cholera

Compiled and Summarized by AnthonyCholera (or Asiatic cholera or epidemic cholera) is an extreme diarrheal disease caused by the bacterium Vibrio cholerae. Transmission to humans is by ingesting contaminated water or food. The major reservoir for cholera was long assumed to be humans, but some evidence suggests that it is the aquatic environment.

V. cholerum is a Gram-negative bacteria which produces cholera toxin, an enterotoxin, whose action on the mucosal epithelium lining of the small intestine is responsible for the characteristic massive diarrhea of the disease. In its most severe forms, cholera is one of the most rapidly fatal illnesses known—a healthy person may become hypotensive within an hour of the onset of symptoms and may die within 2-3 hours if no treatment is provided. More commonly, the disease progresses from the first liquid stool to shock in 4-12 hours, with death following in 18 hours to several days without rehydration treatment.

Signs and Symptoms

Symptoms include those of general GI tract (stomach) upset and massive watery diarrhea. Symptoms may also include terrible muscle and stomach cramps, vomiting and fever in early stages. In a later stage, the diarrhea becomes "rice water stool" (almost clear with flecks of white). Radical dehydration can bring death within a day through collapse of the circulatory system.

Persons infected with cholera have massive diarrhea. This highly liquid diarrhea is loaded with bacteria that can spread under unsanitary conditions to infect water used by other people. Cholera is transmitted from person to person through ingestion of feces contaminated water loaded with the cholera bacterium. The source of the contamination is typically other cholera patients when their untreated diarrhea discharge is allowed to get into waterways or into groundwater or drinking water supply. Any infected water and any foods washed in the water, and shellfish living in the affected waterway can cause an infection. Cholera is rarely spread directly from person to person. V. cholerae occurs naturally in the plankton of fresh, brackish, and salt water, attached primarily to copepods in the zooplankton. Both toxic and non-toxic strains exist. Non-toxic strains can acquire toxicity through a lysogenic bacteriophage. Coastal cholera outbreaks typically follow zooplankton blooms. This makes cholera a zoonosis.

Diagnosis

In order to make a cholera diagnosis, the doctor will ask a number of questions about the following topics:

* Recent history of foods or drinks that have been consumed * Recent travel history * Current medical conditions * Current medicines.

As part of making a cholera diagnosis, the doctor will also perform a physical exam to look for signs of cholera and fluid loss. If the doctor suspects cholera, he or she will ask for a stool sample.

Looking at a stool sample under a microscope can help the doctor make a cholera diagnosis. He or she will be looking for Vibrio cholerae (the bacteria that cause cholera) within the stool. The stool sample can also be sent to a laboratory for analysis.

Incubation Period

The incubation period is from a few hours to five days. It is usually two to three days.

Pathogenesis

Cholera is transmitted by the fecal-oral route. Vibrios are sensitive to acid, and most die in the stomach. Surviving virulent organisms may adhere to and colonize the small bowel, where they secrete the potent cholera enterotoxin (CT, also called "choleragen"). This toxin binds to the plasma membrane of intestinal epithelial cells and releases an enzymatically active subunit that causes a rise in cyclic adenosine 51-monophosphate (cAMP) production. The resulting high intracellular cAMP level causes massive secretion of electrolytes and water into the intestinal lumen.

Pathophysiology

Symptoms are caused by massive body fluid loss induced by the enterotoxins that V. cholerae produces. The main enterotoxin, known as cholera toxin, interacts with G proteins and cyclic AMP in the intestinal lining to open cl -ion channels. The toxin actually catalyzes the covalent modification of Gαs protein by transferring an ADP-ribose to an arginine residue at the GTPase active site. This ADP-ribosylation prevents Gαs from hydrolyzing GTP, thus causing the protein to become permanently activated. As ions flow into the intestinal lumen (lining), body fluids (mostly water) flow out of the body due to osmosis leading to massive diarrhea as the fluid is expelled from the body. The body is "tricked" into releasing massive amounts of fluid into the small intestine which is expelled in up to thirty-six liters of diarrhea over a six day period in adults, resulting in massive dehydration.

Prevention

Although cholera can be life-threatening, it is nearly always easily prevented, in principle, if proper sanitation practices are followed. In the United States and Western Europe, because of advanced water treatment and sanitation systems, cholera is no longer a major threat. The last major outbreak of cholera in the United States was in 1911. However, everyone, especially travelers, should be aware of how the disease is transmitted and what can be done to prevent it. Good sanitation practices, if instituted in time, are usually sufficient to stop an epidemic. There are several points along the transmission path at which the spread may be halted:

* Sickbed: Proper disposal and treatment of the germ infected fecal waste (and all clothing and bedding that come in contact with it) produced by cholera victims is of primary importance.

* Sewage: Treatment of general sewage before it enters the waterways or underground water supplies prevent possible undetected patients from spreading the disease.

* Sources: Warnings about cholera contamination posted around contaminated water sources with directions on how to decontaminate the water.

* Sterilization: Boiling, filtering, and chlorination of water kill the bacteria produced by cholera patients and prevent infections, when they do occur, from spreading. All materials (clothing, bedding, etc.) that come in contact with cholera patients should be sterilized in hot water using (if possible) chlorine bleach. Hands, etc. that touch cholera patients or their clothing etc. should be thoroughly cleaned and sterilized. All water used for drinking, washing or cooking should be sterilized by boiling or chlorination in any area where cholera may be present. Water filtration, chlorination and boiling are by far the most effective means of halting transmission. Cloth filters, though very basic, have greatly reduced the occurrence of cholera when used in poor villages in Bangladesh that rely on untreated surface water. In general, public health education and good sanitation practices are the limiting factors in preventing transmission.

Treatment

Cholera is an easily treatable disease. The prompt administration of oral rehydration salts to replace lost fluids nearly always results in cure. In especially severe cases, intravenous administration of fluids may be required to save the patient's life.

Left untreated, however, cholera can kill quickly following the onset of symptoms. This can happen at a speed that has incited fear and paralyzed commerce throughout history. Although such reactions are no longer justified, cholera continues to be perceived by many as a deadly and highly contagious threat that can spread through international trade in food.

o Dehydration, which may lead to renal failure and death, is the most important complication.

o Another complication is electrolyte imbalance if appropriate solutions (eg, those recommended by the WHO) are not used for rehydration.

o Hypoglycemia is an important complication that should be evaluated for and treated with glucose therapy. Use of glucose-containing solutions, such as lactated Ringer solution, and avoidance of isotonic sodium chloride solution for rehydration can prevent hypoglycemia.

Complications of therapy: Overhydration with parenteral fluid therapy presents with the earliest sign of puffiness of eyelids. If not recognized at this stage, it may lead to pulmonary edema.